Preparation of apertured metal screens



Dec. 15, 1953 e. K. TEAL PREPARATION OF APERTURED METAL SCREENS 3 Sheets-Sheet 1 Original Filed Dec.

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lA/VENTOR G. K TEAL ATTORNEY Dec. 15, 1953 G. K. TEAL 2,662,274

PREPARATION OF APERTURED METAL SCREENS Original Filed Dec. 29. 1948 3 Sheets-Sheet 2 FIG. /2

FIG. [4

EVIPOIMTZ' INVEL N701? a. x. r541.

ATmP/VEV Dec. 15, 1953 G. K. TEAL 2,662,274

PREPARATION OF APERTURED METAL SCREENS Original Filed Dec. 29, 1948 '5 Sheets-Sheet s 00000000000 500: 6/ o o O 0 O 0 O O 0 O O 53 J OXYGEN ATMOSPHERE S/L YER ELECTRODE.

| ',CU/7-ENT DISCIIARGE' ALUMINUM ELECTRODE f L60 m/vmmn G. K TEAL ATTORNEY Patented Dec. 15, 1953 PREPARATION OF APERTURED METAL SCREENS Gordon K. Teal, Summit, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Original application December 29, 1948, Serial No. 67,917. Divided and this application October 27, 1949, Serial N 0. 123,873

3 Claims.

This invention relates to electro-optical devices and more specifically to methods of making apertured metal screens which can be used, for example, in the production of target or screen structures for use in television transmitter tubes. This application is a division of application Serial No. 67,917, filed December 29, 1948.

It has long been recognized in the development of electron camera tubes for generating picture signals at a television transmitting station that there are many advantages in projecting an electron image of the object for transmission onto one side of the screen of the tube and scanning the opposite side of the screen with a cathoderay beam formed in the tube. An example of a camera tube employing such a two-sided target or screen is the so-called image orthicon tub-e, described in an article entitled The image orthicona sensitive television pick-up tube by Albert Rose, Paul K. Weimer and Harold B. Law, appearing in the July 1946 issue of the Proceedings of the I. R. E., beginning on page 424. The two-sided target makes possible the separation of charging and discharging processes so that the sensitizing procedures and electric fields appropriate to each can be incorporated in the tube without mutual interference. The target must conduct charges between its two sides or surfaces but not along either surface. Moreover, it should have a conducting element therein or nearby to act as the common capacitor plate for the separate picture elements. It has been found very diiiicult to construct satisfactory commercial targets of this type.

It is an object of the present invention to provide novel and improved methods for making apertured metal screens which can be used, for example, in the production of two-sided electron camera tube targets which have a large number of discrete conducting elements per square inch.

In an exemplary method of making an apertured metal screen in accordance with the invention which can be used in the production of a two-sided mosaic target for camera tubes and the like, a thin metal film is formed on a wax block and then very small, hard particles are insuifiated onto the film and pressed into it leaving a perforated screen on the surface. A thick coating of a suitable metal such as nickel is then electroplated on the screen without closing up 2 in which the apertured metal screen of this invention can be utilized.

The invention will be more readily understood by referring to the following description taken in connection with the accompanying drawings forming a part thereof in which:

Figs. 1 to 6, inclusive, illustrate various steps in a process of producing an apertured metallic screen in accordance with the invention;

Figs. 7 to 11, inclusive, illustrate steps in the process of electrolytically polishing the screen shown in Fig. 6;

Figs. 12 to 16, inclusive, illustrate a method of increasing the number of holes in the screen shown in Fig. 11;

Figs. 17 to 20, inclusive, illustrate a method of filling the apertures in the screen shown in Fig. 16

Referring more specifically to the drawings,

Figs. 21 and 22 show, by way of example for purposes of illustrating one use of an apertured metal screen made in accordance with the invention, portions of a two-sided mosaic target 30 suitable for use in certain television transmitting tubes, such as, for example, the image orthicon type of tube briefly referred to above. It will be understood that Figs. 21 and 22 are merely schematic showings and the same applies to the other figures in the drawings. Target 30 comprises a. thin metallic screen 53 of a suitable metallic material having a large number of holes to the linear inch, e. g., four hundred per inch or more. One surface, such as the top surface in Fig. 22, and the interiors of all the apertures in the screen 53 are coated with an insulating material 54. The interiors of all these apertures are filled with metallic plugs 51A. Successive steps in the preparation of the screen or target 30 will be easily understood by referring to Figs. 1 to 20, inclusive, in some of which for simplicity in the drawings, the structure around one aperture only has been shown.

The first six figures of the drawings illustrate schematically a method in accordance with the invention of forming a metallic screen having a number of apertures therein. Fig. 1 shows a thin conducting layer 40 of platinum or other suithat or curved plate.

able material which is evaporated, sprayed, sputtered or otherwise deposited on a wax block 4|. Very small particles of uniform diameter are insufliated upon the surface of the film 40. These particles 42 may be any hard particle, such as diamond, sapphire, iron, nickel or other solid. Fig. 2 showsthese. particles on theconducting film 40.

As shown in Fig. 3, the particles 42 are pressed into the metal film 40 with a roller or a smooth This breaks small areasof the metal 40 away from the main part of the conducting film leaving thereby .9, perforated screen on the surface of thewax. :Small areas 43 of the screen are pressed into the wax-block 4|.

If the particles 42 are conductors such as: iron or nickel, they may be dissolved withsnitric: or

hydrochloric acids. If the particles 42 are insulating particles this step can be omitted.

As thick a coat of nickel is applied to the platinum screenAll, as, is possible without, closing up the holes 44. The coating i45 is,shown,'in Fig. 5.

The metal screen of ,Fig. 6 is lsuitablefor .a

variety of purposes but one particular use .will

now be described'hy wayof example.

Let it be assumed thatan. enlarged side view of onenof the, apei'turesl44 and of "its surrounding metal is shown in Fig.'f' 7, .and. a large ,,cross section of the aperture, Lie-shown in Fig.1 It is obviousthatthe actualiaperture 44 is by. no

means as smooth as is represented iniFig."7. It

sulfuric acid'and water (120 cc. :l-I2SO4 to 180 cc. H2O) "at ahigh current density. Thisiroun'ds off some'ofthe projectionsand dissolvesjpartof the nickel screen.as indicated inFigs. .9 and '10 whichotherwise correspond toiFigs. 7 a'n'd'S, respectively. A thin film of metaliisithen electroplated upon the screen'46 and-the polishing. procass is repeated and rte-repeated as often .as'neces- .sary to give the smoothscreen twishownf'inFig.

11. It willbe noted'that in'l igs. 7'1to11,'inclusive, no attempt has been: made to 'show' the various metal'layers (such as, for'exampla'layers 45* and' 40) .making up the screen; itbeingshown for simplicity "merely as ta :solid metal screen 46.

Figs. ':1- 2 to 16, inclusive, illustrate a' method of increasing the number of holes-in the screen 46. Asshown in Fig. '12,1the *m'etalscreenflfi shown iii-Fig: 11' is: placed uponand in-intimate contact withapiece of thin filter material '41, such as "paper, and fa metal "or other "soli'd'is evaporated through 'the holes *44 in "the screen. This'givesapattern of'thin solid dots "48 over theientire surface iof ltheipaper as indicated. in Fig. 13. Obviouslythe",dotsare not perfect circles'as jshown in"F ig.I13\but are shown thuslfor simplicity .in the drawings.

,The screen 46 is then shifted into 'positionIso that'the holes 4.4 fall in the 1 positions indicated by the clear-circles 149AjinjFig. 14, and alsolid is'evaporated through the 'holes'in the screen whileitis inthispositionto produce new thin soliddots 49' (shown in Fig.}16).

TheLmetalscreen-AS is' then removed and the filter paperfilupon which alumin'um'dotsl ia and have been superimposed is'pla ce dupon-a filter 4. cylinder 5i! of sintered glass or glass containing a multiplicity of capillary holes and a layer of silver oxide or copper oxide 5! is deposited upon the paper while vacuum is applied to the underside of the cylinder. The entire assembly is then placed in a reducing atmosphere and the silver .oxide or copperpxide reducedto. either silver or copper. ,The aluminum dots 48 and 49 are now .et'ched out ofthe holes with concentrated potas- 'sium hydroxide solution giving a perforated metal screen having twice the number of holes possessed by the original screen.

;The.metal screenproduced by the process illus- -.trated..by:Ffigs.;12-to 15, inclusive, is now used in the repetition of :this procedude to produce a imetal screen having. holes including those shown ;as 48;;and 49 iinz'Fig. 14 and also those shown lin..the.-portions:ofithe dotted circles 52 in Fig.

16. This; produces a screen shown as 53 in Fig. 17 which contains four times the total number of. holesas the screen shown in Fig. 12 and twice the number. of holes per. linear inch as that shown inEig. 12.

"Figs.j17' to"20, inclusive, illustrate amethod of filling the aperturesinthe screen '53 withinjsulatedmetallic'plugs. Referring now to Fig. 17, the metal screen';53 is'coated withinsulating layer 54. This is obtained by condensing the vapor'of a 'suitablejsubstance such as'cryolite 'on' the top of the'screen' orby insuiliatingjglass on the screen and then' fusing it tcgive the coating 54. A uniform'coating of beeswaxasphaltum or other adhesive" 55 is appliedto. a fairly"thick stiif piece of metal or glass 'iifi. "The .adhesiveis ifiowed'on the'metalbr glassfifi "byg'melting-oraby use of a solution of the adhesive-ima solvent'such as carbon-tetrachloride. Evenness' ofspreading can beiassured icy-spinning. in a horizontal plane. The coated'metal :screen 53 is pressed ontothe wax filmf55 so that :asmall. amount 55A of the wax is pushedinto'each 'holetof the screen as shown infFig.t17. j Silverjoxide" 51 isthenJapplied' to the surface of "the .unit "of "Fig. 17 :by "bombarding silver in oxygen with high "voltage discharges. Thiscanbeaccomiolishedin the apparatus shown in'Fig.,23" wherein'jthe unit 58 shown inLFig. 117 and represented ls'chematically', by a. rectangle in figj23mountedin1the path between a silver electrodeiia' and. an aluminum electrode 6 01in an oxygenatmo'sphere, a sourceof high direct-current voltage .6 If being .Jc'onnected between the two electrodes. LBeCause'bLtheoXygen atmospherea multiplicity of silver-lioxideparticles51. is builtup inthe apertures'or the unit" 53.

.Theexcess. silver. oxideis then wipedoff leaving thesilver. oxide plugsfillinfthe holes of the screen 53 as -show'1iinFigJ19. .Theu'm't is then heated up and the. screenns removedfrom its support.

7 The .-screen of Fig. 19 is then-heated in hydrogerrto reduce thez silver oxide. 51 to silver buttons .l5lA. .Alternativeiy,-;it canbetreated with a-liquid reclucing agent like oneof those frequently used 2 in photography, for example. This produces .a screen one elemental portion of which is shown-in :Fig. 20 and another larger portion of which isshownto arso mewhat smaller scale in Figs 21 and12 2. 7 v

.Various alternative'steps-andprocedures other than thosementionedfabove are-of course possible without departing Trom :the spirit of the invention, .the scope .of which is pointed out in the .claims. The .disclosed over-all process -015 making .rnosaic screens -of the type shown in Figs..-21 and.- 22 claimed in-theparent applicaa s r a lla led Decem r 29,1948;

the methods disclosed herein of electrolytically polishing apertured metal screens (Figs. 7 to 11, inclusive) are claimed in a copending application of the present inventor, Serial No. 123,874, filed October 27, 1949, the methods disclosed herein of increasing the number of holes in apertured metal screens (Figs. 12 to 16, inclusive) are claimed in another copending application of the present inventor, Serial No. 123,875, filed October 27, 1949; and the sputtering method disclosed herein and the apparatus used therefor (Figs. 17 to 20, inclusive, and 23) are being claimed in still another copending application of the present inventor, Serial No. 123,876, filed October 2'7, 1949.

What is claimed is:

1. The method of making an apertured screen having at least 400 holes to the linear inch for an electron camera tube target comprising the steps of placing a thin metal layer on a support member, insufilating a large number of very small hard particles on said metal layer, pressing the particles into and through said metal layer thereby forcing portions thereof into said support, removing the particles from the apertures produced thereby, and thickening by electroplating the thin apertured metal screen produced by said pressing.

2. The method of making an apertured screen having at least 400 holes to the linear inch for an electron camera tube target comprising the steps of placing a thin metal layer on a support member, insufiiating a large number of very small hard particles on said metal layer, pressing the particles into and through said metal layer thereby forcing portions thereof into said support, removing the particles from the apertures produced thereby, and coating a layer of metal on the apertured thin metal layer.

3. The method of making an apertured screen having at least 400 holes to the linear inch for an electron camera tube target comprising the steps of placing a thin metal layer on a support member, insufllating a large number of very small metal particles on said metal layer, pressing the particles into and through said metal layer thereby forcing portions thereof into said support, dissolving in acid the metal particles in the apertures produced thereby, and thickening by electroplating the thin apertured metal screen produced by said pressing.

GORDON K. TEAL.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,116,776 Wilcox Nov. 10, 1914 1,379,036 Moorhead May 24, 1921 2,226,384 Norris Dec. 24, 1940 2,252,823 Wallace Aug. 9, 1941 2,266,349 Wempe Dec. 16, 1941 2,419,862 Wales Apr. 29, 1947 2,424,087 Focke et a1 July 15, 1947 2,499,977 Scott Mar. 7, 1950 

